THE DEVELOPMENT OF THE INTEGUMENTARY SYSTEM. 



441 



the first and second years after), except over the face, and is replaced by coarser 

 hairs. These in turn are constantly being shed during the life of the individual 



t 







\ ^m^7 MM 



\^^p^r ^m 



l s^*&* i 



>V f tr<-2&? : ***f& '<< 



^ ft 



FIG. 393. Five stages in the development of a human hair. 

 C, Papilla; 5, arrector pili muscle; c, beginning of hair shaft; d, point where hair shaft grows 

 through epidermis; e, anlage of sebaceous gland; /, hair germ; g, hair shaft; h, Henle's 

 layer; , Huxley's layer; k, cuticle of root sheath; /, inner root sheath; m, outer root sheath 

 in tangential section; n, outer root sheath; o, connective tissue follicle. 



and replaced by new ones. The new hairs probably in most cases develop from 

 the old follicles, the cells over the old papillae proliferating and the newly 



